This invention relates to lead mining, or more particularly to the processing of lead ores containing galena and associated sulfide minerals and for the remediation of lead waste tailings. The invention also finds use in the remediation of lead contaminated soils, sludges, and sediments.
At present there are hundreds of thousands of hazardous waste sites wherein lead is the most prevalent heavy metal contaminant. Many abandoned mine waste piles exist which contain residual lead deposits including sphalerite, chalcopyrite, and galena. There is therefore a great need for the clean processing of lead ores and for cleaning up of existing wastes to protect the environment. Many processing materials currently used in the lead processing industry are toxic. Therefore there is a great need for developing less toxic substances to be used in the processing of lead.
Many techniques for froth flotation of lead sulfide materials are well known in the art. Froth floatation renders the surface of the mineral to be collected hydrophobic and hence floatable. Previously known or used methods of galena flotation employ thiol collectors to render the galena surfaces hydrophobic. These thiol collectors include xanthates, mercaptans, thiocarbamates, trithiocarbonates, dithiophosphates, diphenyl thiourea, and mercaptobenzothiazole. All of these materials and their derivatives are highly toxic to animals, plants, and humans.
This invention substitutes rapeseed oil for the aforesaid thiol collectors. Rapeseed oil, also known commercially as Canola oil, is approximately 10 times less toxic than the thiol collectors and is considered essentially nontoxic to humans. Rapeseed oil is so nontoxic that it is listed as a food additive by the U.S. Food and Drug Administration.
A further problem in the art is that lead sulfides are normally present in ores together with iron containing minerals. Prior art froth floatation techniques are insufficiently selective to discriminate between lead sulfides and iron containing minerals. This invention provides an improved method of processing lead sulfide minerals using froth flotation which has a high selectivity against the iron minerals normally present in sulfide deposits.
Hence, the important advantages of this invention over the prior art are reduced toxicity and high specificity against the iron minerals present in the feed. The invention can also be used by lead mineral processors where there is an extreme concern for the environment and strict discharge limits for the processing plants.